I think I was assaulted

Aged 15, pretty screwed up from an emotionally abusive father - felt unlovable, unattractive. Discovered alcohol would change me, people (men) would be interested in me.

One of them 5 years older waited until I was very drunk, led me away and the next thing I remember was that he was making me perform a sexual act on him - he used to do it every weekend, would wait until I was drunk then lead me away.

For so long I have blamed myself, because I let it happen more than once. But now as an adult I wonder if maybe this wasn't OK for him to do this.

I'm not sure what you can do about it at this point… I don't really know much about reporting it to the police.
I guess it's still possible, though.

But the important thing is that you not feel 'screwed up', and make sure you're looking after yourself.
Are you still drinking? Because if you are and you've recognized the problem, it's time to start taking control of your life.